Glass fibre is a form of glass produced by a technique in which molten glass is passed through a multi apertured mould to form filaments. These filaments have: small diameters usually in the range of 1 micron to 4 micron, typically about 2 micron, although diameters outside this range are known for special applications. These filaments are then subjected to a sizing operation, using a sizing agent, possibly in combination with other additives, to provide bonding of the filaments together to form strands or fibres.
One application of glass fibres is to provide reinforcement and flexibility to thermoplastic polymer articles, typically made of polymers such as polypropylene, polyamides and polycarbonates, and usually shaped by injection moulding.
The sizing agent additionally functions to protect the filaments from breaking during handling, and must also be To obtain the most efficient sizing of glass filaments, the emulsion should be free of particles above 2 microns, and preferably has a weight mean particle diameter of above about 0.2. micron, more preferably above about 0.4 micron. Mean weight particle diameters of the copolymer particles are typically in the range of 0.4 to 1.0 micron.
Examples of the acrylate monomers are methyl methacrylate (homopolymer Tg of 100 .degree. C.), ethylhexyl acrylate (Tg of -60 .degree. C.), butyl acrylate (Tg of -50.degree. C.) and ethyl acrylate (Tg of -22.degree. C.). A proportion of a carboxylic monomer, for example acrylic acid, may also be present to improve adhesion to the surface of glass. Other monomers may be incorporated at minor levels, that is up to 10% by weight of the total monomers, usually up to 5%. Examples of these monomers are vinyl silanes, cross linking agents and epoxy monomers, e.g. glycidylmethacrylate. The cross linking agents may be capable of internal cross linking, e.g. diallyl maleate, triallyl cyanurate or crosslinkable, e.g. N-methylolacrylamide.
The acrylate monomer is generally initially present in the form of an emulsion which requires to be stabilised by a protective colloid, and the preferred colloid material is polyvinyl alcohol. There is no criticality in the degree of hydrolysis of polyvinyl alcohol; preferably the degree of hydrolysis is above 70%, and the degree of polymerisation is preferably above 550.
Other protective colloids which can be used include hydroxyethyl cellulose, carboxymethyl cellulose, ethoxylated starch derivatives, polyacrylates, acrylamides, gelatins, alginates, gums and agar. capable of withstanding the heat applied, e.g. up to 200.degree. C., during contact with the polymeric material to be reinforced.